Is it permissible to believe that one's lot is bad or that one does not achieve what one desires, and how can one get rid of this feeling?

It is impermissible to believe in bad luck and pessimism, for it is a discontent with divine decrees and a negative assumption about Allah. A servant must rid himself of this feeling and know that Allah is Self-Sufficient, Praiseworthy, Wise, placing things in their rightful places. He may withhold a gift for a wisdom and benefit that He, Exalted be He, knows, in accordance with His saying: "But perhaps you hate a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allah knows, while you know not." (Al-Baqarah: 216).

A servant must entrust his affairs to Allah and trust in His management, for Allah is more merciful to His servant than a mother is to her child, and more knowledgeable of his interests. His choice for the servant is better than the servant's choice for himself. Objecting to destiny stems from a negative assumption about Allah.

Ibn al-Qayyim states that most people assume ill of Allah, believing that they are deprived of their rights and lack good fortune, and that they deserve more than what Allah has given them. This is a reproach of destiny. A person should repent and seek Allah's forgiveness for this assumption, and instead assume ill of his own self, which is the abode of all evil. For Allah is the Wisest of judges and the Most Merciful of those who show mercy, and all His actions are wisdom, benefit, mercy, and justice.